Intrinsic 2D-XY ferromagnetism in a van der Waals monolayer

Abstract

Taking the measure of a magnet The recent discovery of magnetism in two-dimensional (2D) materials has inspired efforts to understand its nature. Whereas the magnetism of monolayers of chromium iodide (CrI 3 ) can be understood in terms of out-of-plane magnetic anisotropy, the related material chromium chloride (CrCl 3 ) has spins that lie in the plane. Bedoya-Pinto et al . used molecular beam epitaxy to grow monolayers of CrCl 3 on graphene and studied its magnetic properties. Using x-ray magnetic circular dichroism measurements, the authors found that monolayer CrCl 3 is a ferromagnet, unlike bulk CrCl 3 , which is antiferromagnetic. The scaling of the signal in the critical region indicated that the material belongs to the 2D-XY universality class, distinct from Ising magnetism, which some other 2D magnets exhibit. —JS

Unconventional ferrimagnetism and enhanced magnetic ordering temperature in monolayer CrCl3 by introducing O impurities and Cl vacancies

“…The magnetization is mainly localized on the Cr site with little contribution stemming from Cl atoms (Cl magnetic moment is less than 0.10 µ B ). The Cr magnetic moment (3.15 µ B ) is close to the value of metallic Cr [3,4] and the average total magnetic moment results large (2.94 µ B /Cr) for the pristine phase, which is close to previous theoretical [25,30] and experimental [17] results. The magnetism is almost linearly enhanced with the introduction of Cl vacancies.…”

“…These peculiar occurrences are relevant in determining the magnetic properties of this class of 2D materials. Indeed, different studies have highlighted the pivotal role of halogen vacancies in strengthening the ferromagnetic (FM) interaction [12,15] and enhancing the magnetic ordering temperature [16], which is worth to be considered for CrCl 3 , since manifests a FM transition at relatively low temperature (13 K) in the monolayer [17]. Besides, the Curie temperatures (T C ) of Cr trihalides are generally predicted to be raised upon doping [18][19][20] and including oxygen impurities [21].…”

Controlling magnetism through Ising superconductivity in magnetic van der Waals heterostructures

“…The strength of the induced exchange field in the superconductor depends on many factors [37,45,46]. If the induced exchange field is out-of-plane and is larger than the Pauli paramagnetic limit, J > H P , the monolayer TMD remains in the normal state.…”

“…However, the magnitude of J depends on the chosen materials combination, and can also be below the critical field H P . In what follows, we consider a case of the induced exchange field J < H P in the monolayer TMD [9,46,47] so that it becomes superconducting at low enough temperature.…”

“…While the experiment focused on a monolayer CrBr 3 on top of a bulk NbSe 2 , it is worth noting that the value of the exchange proximity would be comparable for a monolayer NbSe 2 given its van der Waals nature. From the point of view of the ferromagnetic insulator candidates, apart from CrBr 3 , CrI 3 [9], CrCl 3 [46], recently synthetized chromium heterohalides [47] would provide excellent candidates. Importantly, van der Waals chromium heterohalides have been demonstrated to have a completely tunable magnetic anisotropy, making them outstanding candidates for our proposal [47].…”